Letter abstract
Nature Materials 8, 803 - 807 (2009)
Published online: 16 August 2009 | doi:10.1038/nmat2511
Subject Categories: Semiconductors | Optical, photonic and optoelectronic materials | Nanoscale materials
Long lifetimes of quantum-dot intersublevel transitions in the terahertz range
E. A. Zibik1,5,6, T. Grange2,5,6, B. A. Carpenter1, N. E. Porter1, R. Ferreira2, G. Bastard2, D. Stehr3, S. Winnerl3, M. Helm3, H. Y. Liu4,5, M. S. Skolnick1 & L. R. Wilson1
Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers1, 2) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 
2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.
- Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, Centre National de la Recherche Scientifique, 24 Rue Lhomond, 75005 Paris, France
- Institute of Ion Beam Physics and Material Research, Forschungszentrum Rossendorf, PO Box 510119, 01314 Dresden, Germany
- EPSRC National Centre for III–V Technologies, Sheffield S1 3JD, UK
- Present addresses: Oclaro (Switzerland) AG, Binzstrasse 17, CH-8045 Zürich, Switzerland (E.A.Z.); Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany (T.G.); Department of Electronic & Electrical Engineering, University College London, London WC1E 7JE, UK (H.Y.L.)
- These authors contributed equally to this work
Correspondence to: R. Ferreira2 e-mail: robson.ferreira@lpa.ens.fr
Correspondence to: L. R. Wilson1 e-mail: Luke.Wilson@sheffield.ac.uk
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